In current industrial practice, known porous silicocalcareous masses are made from a thorough mixture of lime, ground silica or ground fossil silica and asbestos in a suspension water. The resulting paste, introduced in the containers, molds or bottles, is then subjected to heat in an autoclave to initiate and complete the lime-silica reaction which results in producing the silicocalcareous material; this material is then transferred to a drying oven to remove the water and create the desired porosity.
Asbestos is added to the aqueous composition of silica and lime for effecting its function as a reinforcing fiber and suspension agent. However, recent constraints relating to health and safety connected with the handling of asbestos have led to reconsideration of the use of this natural fiber the characteristic properties of which in making porous silicocalcareous masses, function to reinforce the crystalline structure and to aid in maintaining the suspension of the solid products, namely silica and lime, in a large amount of water.
It is known that the stabilization of the suspension can be markedly improved by the use of suspension agents. The effect of adding substantial amounts, up to 10%, of organic suspension agents is known from U.S. Pat. No. 3,406,030. Certain cellulose derivatives such as alkylhydroxyalkyl-celluloses, in particular methyl- and ethylhydroxyethyl-cellulose, make it possible to obtain an excellent stabilization of the suspension. The amount to be introduced varies with the desired degree of stabilization and the nature of the suspension agent.
Compensation for discontinuing use of asbestos by the addition of organic suspension agents in very large amounts has been considered. It has been shown that the addition of an organic suspension agent, in a large amount, can appreciably correct the defect of decanting the solid products during making of the silica/lime and water paste. However, because of the destruction of this type of organic compound during firing of the paste, a decrease in the mechanical properties of the dried high-porosity silicocalcareous masses has been noted. The brittleness, fragility and friability of the resulting porous materials are such that they render them unsuitable for the applications mentioned above.